1. Field of the Invention
This invention relates to the lining of pipes with a cement mortar and more particularly it concerns novel methods and apparatus for carrying out such lining.
2. Description of the Prior Art
U.S. Pat. Nos. 1,988,329 and 2,168,917 to A. G. Perkins illustrate arrangements for lining the interior of pipes with a cement mortar material. As shown in both those patents, a wet cement mortar is thrown centrifugally from a rotating distributor head out against the inner surface of the pipe. When properly applied, the mortar will adhere to the pipe surface until it hardens whereupon it forms a unitary, self supporting structure within the pipe. The Perkins patents also show rotating trowels mounted behind the distributor head to smooth the lining material before it hardens. Additionally, U.S. Pat. No. 1,988,329 shows a rotating spray head through which an asphaltum curing control liquid is pressure sprayed onto the freshly trowelled lining. U.S. Pat. No. 2,168,917 shows an alternative means for applying a curing control liquid, namely a second electrically driven centrifugal distributor head.
U.S. Pat. No. 3,069,093 H. C. Schultz illustrates a machine for lining relatively small diameter pipes. According to this patent, a single motor is used to drive both a cement mortar centrifugal distributor head and a curing control liquid centrifugal distributor head. The two distributor heads are located immediately adjacent each other but the blades on each head are canted in opposite directions so that their sprays do not overlap. The Schultz device does not use a trowel.
U.S. Pat. No. 3,920,363 to Henry A. Nelson Holland shows a pipe lining machine which includes a centrifugal distributor for depositing wet cement mortar onto the interior of a pipe and a non-rotating drag trowel which is pulled along behind the distributor. The Holland patent does not disclose the application of a curing control liquid.
It has been found that when a curing control liquid is properly applied to the surface of a pipe which has just been lined with a cement mortar, the resulting fully cured lining will have greater strength than in cases where no curing control liquid is used. This curing control liquid, which may be, for example, an asphaltum or a liquid bituminous material, forms a moisture barrier on the surface of the mortar and retards the escape of water from the mortar mix. As a result the mortar will cure fully and it will not shrink appreciably during the curing process. The resulting mortar lining therefore has maximum strength and it will remain in close fitting relationship with the surrounding pipe.
Past arrangements and techniques for applying a curing control liquid to a mortar lined pipe have not been satisfactory. One reason for this is that the freshly applied wet mortar does not strongly adhere to the pipe surface; and if the lining is disturbed to any substantial extent before it has taken its initial set and has begun to acquire structural strength of its own, it is likely to result in a "fall" wherein the entire mortar lining pulls away and falls to the bottom of the pipe. Cleanup problems in such case are formidable. Trowelling also disturbs the lining and renders it even more susceptible to a fall. Because of this it has not been recommended to apply a curing control liquid in the manner of the Perkins patents onto a freshly trowelled mortar lining since the force of the curing control liquid being sprayed or thrown against the lining substantially increased the likelihood of a fall.
Because of the foregoing difficulties, curing control liquids were either not used or they were applied only after the mortar lining has taken its initial set and had built up appreciable strength. In the latter case a man (in the case of large diameter pipe) or a machine (in the case of small diameter pipe) would go along inside the pipe and apply the curing control liquid to the partially cured lining. In the case of smaller diameter pipe, an air driven or atomized spray of curing control liquid was previously employed. However the spray nozzle and the liquid and air supply lines had to be supported centrally of the pipe by framework elements which were dragged over the still incompletely cured mortar. These latter techniques also presented difficulties because the curing control liquid was not applied until after the critical initial curing phase (usually twelve to eighteen hours after application). Also, after the initial curing phase, the mortar would cool and condensation would form on the mortar surface and this would often prevent adherence of the curing control liquid.
Another difficulty encountered with the prior art is that of providing a very thin but uniform coating of the curing control liquid on the cement mortar. In the above identified patents to Perkins the spray nozzles or centrifugal distributor for the curing control liquid was mounted on a supply tube which extended out from the mortar distributor head. Also, the mortar distributor head extended out behind the lining machine itself and the lining machine was centered in the pipe by means of wheels which rolled along inside the pipe. When the wheels encountered lateral deviations, e.g. from curves or irregularities inside the pipe the resulting shift of the lining machine axis was multiplied out at the spray nozzle or centrifugal distributor for the curing control liquid. This would result in a variation of the coating on different portions of the lining. This variation was particularly pronounced in small diameter pipes.